// js data type
let num: number = -10;
let str: string = 'hello';
let bln: boolean = true;
let und: undefined = undefined;
let nil: null = null;
let int64: bigint = 9223372036854775807n; // es2020 or later
let sym: symbol = Symbol();
let obj: object = {};

console.log('typeof num ? ', typeof num);
console.log('typeof str ? ', typeof str);
console.log('typeof bln ? ', typeof bln);
console.log('typeof und ? ', typeof und);
console.log('typeof nil ? ', typeof nil);
console.log('typeof int64 ? ', typeof int64);
console.log('typeof sym ? ', typeof sym);
console.log('typeof obj ? ', typeof obj);

console.log('nil === null ? ', nil === null);
console.log('obj instanceof Object ? ', obj instanceof Object);

function plus(num1: number, num2: number): number {
    return num1 + num2;
}

let result = plus(10, 20);
console.log(result);